Combustion nailers are known in the art, and are described in U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 6,145,724, all of which are incorporated by reference herein. Similar tools are available commercially from Illinois Tool Works of Glenview, Ill.
Such tools incorporate a tool housing enclosing a small internal combustion engine or power source. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. Such ancillary processes include: mixing the fuel and air within the chamber; turbulence for increasing the combustion process; scavenging combustion by-products with fresh air; and cooling the engine. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel-metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the combined piston and driver blade is forced downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original or pre-firing position, through differential gas pressures created by cooling of residual combustion gases within the combustion engine. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
After the combustion cycle, also known as the power cycle, is completed, it is followed by an exhaust cycle and thereafter a recharge cycle. During the recharge cycle, the valve sleeve is in the open venting position and the fan motor replaces spent combustion gases with fresh air. For effective and repeatable nailer performance, it is necessary that the recharge cycle has been completed before a subsequent cycle occurs. If spent gases have not been entirely or substantially removed, then during the subsequent operation cycle, combustion will not occur or will be insufficient. This is the result of improper fuel to air ratio caused by exhaust gases diluting the fresh air charge.
Traditionally, combustion-powered tools have been designated as sequentially operated. In other words, the tool must be pressed against the work, collapsing the workpiece contact element (WCE) before the trigger is pulled for the tool to fire or drive a nail. This contrasts with pneumatic tools, which can be fired or activated in a repetitive cycle operational format. In other words, the latter tools will fire repeatedly by pressing the tool against the workpiece, if the trigger is held in the depressed mode. These differences manifest themselves in the number of fasteners that can be fired per second for each style tool and for each mode of operation. Another aspect of sequential operation of combustion nailers is that only after a valve sleeve position switch, commonly referred to as a “chamber switch” and a trigger switch have been closed in the order mentioned and then opened, will a subsequent engine cycle be permitted. Such an operational control, described in U.S. Pat. No. 5,133,329, incorporated by reference, prevents unwanted ignition or other tool feature operations, such as electronic fuel injection (EFI), in instances when both switches remain closed after an engine cycle is complete.
It is known to provide a combustion nailer with the user-controlled option of operation in either sequential or repetitive cycle mode. Such operation is described in co-pending U.S. patent application Ser. No. 11/028,450 filed Jan. 3, 2005, US Patent Application Publication 2005/0173487A1 which is incorporated by reference. To achieve successful operation in the repetitive cycle mode, the tool's valve sleeve must be automatically controlled to maintain a correct combustion sequence in the face of increased firing cycles.
However, in repetitive cycle operation, the control system in some cases may authorize a subsequent ignition even if there has been inadequate opportunity for a satisfactory recharge cycle. Thus, while electronically “authorized”, an actual combustion will not occur, since the combustion chamber gases have not been adequately exchanged or replaced. Subsequently, unwanted operation of the ignition system, EFI or other tool functions may occur, wasting tool resources and possibly shortening tool operational life.
U.S. Pat. No. 6,783,045 discloses a combustion-powered nail gun designed for either sequential or repetitive cycle operation. Included in this device when in repetitive cycle (“successive shot”) operation, is a successive shot timer which is triggered upon ignition. The successive shot timer allots a period of time Td2 after ignition during which a successive ignition is prevented. Functions of the period Td2 are for allowing time for the piston to drive a fastener and return to the prefiring position, and also for allowing for the exhaust gas in the combustion chamber to be replaced with fresh air. The '045 patent recognizes that if ignition is permitted prior to the expiration of Td2, a failed ignition may result.
However, despite the allotment of time Td2, it is likely that a user operating the tool at a rapid rate will lift the nailer quickly from one site of a fastener application, opening the combustion chamber quickly but insufficiently to effectively replace the exhaust gas with fresh air. The user then progresses to the next fastening site and presses the tool against the workpiece so that the combustion chamber is sealed for the next engine combustion cycle. Since the combustion chamber was not effectively recharged with fresh air, the subsequent combustion cycle and fastener drive will be ineffective, thereby wasting fuel, battery power, and possibly spoiling the work piece. It will be seen that merely allocating a period of time after ignition for the recharging of combustion chamber gas will not ensure that the recharge has taken place.
Thus, there is a need for an improved control system for a combustion nailer, wherein the control system prevents tool operation unless the recharge cycle is completed, regardless of whether the tool is in a repetitive or a sequential operational mode. There is also a need for an improved control system for a combustion nailer that conserves tool power resources unless desired conditions are present for subsequent engine combustion cycles. Additionally, there is a need for improved valve sleeve position monitoring to assure the recharge cycle is complete.